1. Field of the Invention
The present invention relates to a method of manufacturing an optical fiber with chiralic structure and the device for putting such a method into practice.
The monomode fibers usually manufactured for telecommunications always have a small amount of linear birefringence and of circular birefringence. Consequently, these fibers keep neither linear polarization nor circular polarization.
It is possible to make the fiber very linear birefringent by breaking the circular symmetry to the benefit of a planar symmetry.
It is also possible to consider a reverse method, which consists in introducing a high circular birefringence so as to keep the circular polarization.
2. Description of the Prior Art
One solution for creating this circular polarization consists in subjecting the glass fiber to a static twisting force, for example applied externally by twisting between its two ends: one effect of twisting this fiber is to introduce therein a circular birefringence.
An optical fiber for maintaining circular polarization is obtained by subjecting the fiber to a static twisting force. One method for manufacturing such a fiber is described in an U.S. Pat. No. 4,427,717: the fiber, at the end of manufacture, is twisted between its two ends and the twisted state thus created is maintained by applying a coating which serves as binding sheath. The method described comprises two variants.
The first consists in twisting and coating the fiber during manufacture thereof and comprises the following steps:
drawing out the fiber; PA1 twisting about the drawing axis; PA1 coating with a rigid material (glass, vitroceramic, metal, plastic) which will freeze the fiber in the twisted state when it becomes solid; PA1 possible coating with a protecting material if the product previously deposited is glass or a vitroceramic. PA1 drawing out the fiber, PA1 twisting, PA1 coating with a rigid material for maintaining the twisted state, PA1 coating with a protecting material. PA1 a step for twisting this fiber about its axis of symmetry at a temperature less than the vitreous transition temperature of this fiber; PA1 a step for coating with a polymer in the viscous state so as to form an envelope for this fiber; PA1 and a step for curing this polymer by increasing its YOUNG's modulus until a modulus is obtained situated in the range: 1 Giga Pascal, 100 Giga Pascal.
The second consists in twisting and coating a fiber after manufacture thereof and comprises the following steps:
To apply this process, it is necessary to have a fiber drawing machine.